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README.md
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README.md
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<img src="https://raw.githubusercontent.com/janet-lang/janet/master/assets/janet-w200.png" alt="Janet logo" width=200 align="left">
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**Janet** is a functional and imperative programming language and bytecode interpreter. It is a
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Lisp-like language, but lists are replaced
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by other data structures (arrays, tables (hash table), struct (immutable hash table), tuples).
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The language also supports bridging to native code written in C, meta-programming with macros, and bytecode assembly.
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**Janet** is a dynamic language and bytecode interpreter for system scripting, expressive automation, and
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extending programs written in C or C++ with user scripting capabilities.
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There is a REPL for trying out the language, as well as the ability
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to run script files. This client program is separate from the core runtime, so
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@ -21,14 +19,104 @@ If you'd like to financially support the ongoing development of Janet, consider
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<br>
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## Examples
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See the examples directory for all provided example programs.
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### Game of Life
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```janet
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# John Conway's Game of Life
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(def- window
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(seq [x :range [-1 2]
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y :range [-1 2]
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:when (not (and (zero? x) (zero? y)))]
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[x y]))
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(defn- neighbors
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[[x y]]
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(map (fn [[x1 y1]] [(+ x x1) (+ y y1)]) window))
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(defn tick
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"Get the next state in the Game Of Life."
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[state]
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(def cell-set (frequencies state))
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(def neighbor-set (frequencies (mapcat neighbors state)))
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(seq [coord :keys neighbor-set
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:let [count (get neighbor-set coord)]
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:when (or (= count 3) (and (get cell-set coord) (= count 2)))]
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coord))
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(defn draw
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"Draw cells in the game of life from (x1, y1) to (x2, y2)"
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[state x1 y1 x2 y2]
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(def cellset @{})
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(each cell state (put cellset cell true))
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(loop [x :range [x1 (+ 1 x2)]
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:after (print)
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y :range [y1 (+ 1 y2)]]
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(file/write stdout (if (get cellset [x y]) "X " ". ")))
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(print))
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# Print the first 20 generations of a glider
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(var *state* '[(0 0) (-1 0) (1 0) (1 1) (0 2)])
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(for i 0 20
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(print "generation " i)
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(draw *state* -7 -7 7 7)
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(set *state* (tick *state*)))
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```
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### TCP Echo Server
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```janet
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# A simple TCP echo server using the built-in socket networking and event loop.
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(defn handler
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"Simple handler for connections."
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[stream]
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(defer (:close stream)
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(def id (gensym))
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(def b @"")
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(print "Connection " id "!")
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(while (:read stream 1024 b)
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(printf " %v -> %v" id b)
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(:write stream b)
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(buffer/clear b))
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(printf "Done %v!" id)
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(ev/sleep 0.5)))
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(net/server "127.0.0.1" "8000" handler)
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```
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### Windows FFI Hello, World!
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```janet
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# Use the FFI to popup a Windows message box - no C required
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(ffi/context "user32.dll")
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(ffi/defbind MessageBoxA :int
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[w :ptr text :string cap :string typ :int])
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(MessageBoxA nil "Hello, World!" "Test" 0)
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```
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## Use Cases
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Janet makes a good system scripting language, or a language to embed in other programs.
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It's like Lua and Guile in that regard. It has more built-in functionality and a richer core language than
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Lua, but smaller than GNU Guile or Python.
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Lua, but smaller than GNU Guile or Python. However, it is much easier to embed and port than these languages.
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## Features
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* 600+ functions and macros in the core library
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* Build in socket networking, threading, subprocesses, and more.
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* Parsing Expression Grammars (PEG) engine as a more robust Regex alternative
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* Macros
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* Per-thread event loop for efficient IO (epoll/IOCP/kqueue)
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* Built-in C FFI lets you load existing binaries and run them.
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* Erlang-style supervision trees that integrate with the event loop
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* Configurable at build time - turn features on or off for a smaller or more featureful build
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* Minimal setup - one binary and you are good to go!
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* First-class closures
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@ -38,19 +126,12 @@ Lua, but smaller than GNU Guile or Python.
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* Mutable and immutable arrays (array/tuple)
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* Mutable and immutable hashtables (table/struct)
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* Mutable and immutable strings (buffer/string)
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* Macros
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* Multithreading
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* Per-thread event loop for efficient evented IO
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* Bytecode interpreter with an assembly interface, as well as bytecode verification
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* Tail-call optimization
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* Direct interop with C via abstract types and C functions
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* Interface with C via abstract types and C functions
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* Dynamically load C libraries
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* Functional and imperative standard library
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* Lexical scoping
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* Imperative programming as well as functional
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* REPL
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* Parsing Expression Grammars built into the core library
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* 400+ functions and macros in the core library
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* Embedding Janet in other programs
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* Interactive environment with detailed stack traces
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@ -240,10 +321,6 @@ there is no need for dynamic modules, add the define
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See the [Embedding Section](https://janet-lang.org/capi/embedding.html) on the website for more information.
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## Examples
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See the examples directory for some example Janet code.
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## Discussion
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Feel free to ask questions and join the discussion on the [Janet Gitter channel](https://gitter.im/janet-language/community).
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